Dark net child sex abuse images 'epidemic'
19 June 2014 Last updated at 12:38 BST
Images of child abuse have become "an epidemic" according to one senior police officer in the United States.
He spoke after a BBC investigation found that thousands of paedophiles are operating on the so-called dark net.
The criminals use this hidden network to share indecent images of children, making them very difficult to trace.
Angus Crawford reports from Los Angeles.